Increasingly, in technologies which employ beams of light for transmission of data, or for other communications, fiber optics are being employed. Since the fiber optic element is fragile, one or more fiber optic elements are placed into a bundle which is inserted into a protective buffer tube such as a polyethylene jacket.
The fiber optic elements, however, cannot be allowed to remain loose in a buffer tube. If such were permitted, then almost any kind of mechanical shock or bending could result in damage to or breakage of the fiber optic element. In view of the substantial length of many of the presently used fiber optic elements in data transmission cables, replacement or repair of the fiber optic elements would be both difficult and expensive. Accordingly, means must be provided for cushioning of the fiber optic elements within the buffer tube.
In providing lubrication for or cushioning of the fiber optic elements carried in the buffer tube, care must be taken to assure that the optical qualities of the fiber optic elements are not diminished. Thus, in formulating a filling composition such as a gelled-oil for use with fiber optic elements carried in a buffer tube, the gelled-oil must provide not only lubrication or cushioning, but also must not deleteriously affect the optical qualities of the fiber optic element. Moreover, the gelled oil must not attack the buffer tube or cable housing.
The requirements of gelled oils useful as buffer tube gels and filling compounds for optical cables are not easily satisfied. The gelled oil compounds must remain stable throughout the temperature range of use of the cable, which should extend at least from -40.degree. to +70.degree. C. If the cable is subjected to temperatures higher than the working temperature range but not so high as to injure any of the components of the cable, the filling compounds must be fluid enough for the cable to be formed and completely filled with the compound without risk of breaking or over-stressing the optical fibers.
The gelled oils also should be cohesive enough to ensure that bending of the cable at a radius of a few decimeters or less will not result in the formation of voids in either the interior or surface of the compound. Also, the gelled oils should be soft enough to allow such bending without subjecting the optical fibre elements to any significant strain (since strain causes signal attenuation) but yet resist flow under gravity as well as the hydrostatic pressures likely to be applied to the cable if one of its ends is exposed in a flooded manhole.
It is known in the art that gelling agents such as clays and hydrophobic fumed silica may be employed to provide gelled oil formulations. Hydrophobic fumed silica, however, is expensive since relatively large amounts of fumed silica must be used to provide useful gels. Use of hydrophobic fumed silicas, moreover, causes the resulting gels to be highly abrasive.
A need therefore exists for gelled oil formulations and greases which have improved lubricating properties and which avoid the abrasiveness of silica based gel formulations.